Police say the Oscar winner does not realise the danger he is in by becoming best friends with the violent Bra Boys mob.

An Australian police source told the Daily Star Sunday: “Russell loves the idea of being a real hard man and not just a movie action star. But he doesn’t know he’s mixing with some seriously dangerous people.”

Crowe and Bra Boys leaders and professional surfers Koby, Jai and Sunny Abberton have been the toast of trendy US movie circles thanks to a documentary about the trio narrated by the Aussie film star.

Crowe, 43, is such a fan of the Abbertons he’s rumoured to be planning a big-budget movie version of their lives.

But the brothers have a violent past. Jai, 34, admitted shooting Sydney gangster Anthony Hines three times in the head but was sensationally cleared of his murder in 2003.

Hines’ naked body was found riddled with bullets at the bottom of a cliff.

Brother Koby, 30, was convicted of perverting the course of justice over the case and was given a suspended nine-month jail term.

The brothers’ mum was a heroin addict. Her boyfriend, who Koby treated as a dad, was a bank robber who served 12 years behind bars.

Koby said his mum’s partner chased him out of the house with a baseball bat. He then formed the Bra Boys with his brothers to drive heroin out of Maroubra, a Sydney suburb where they grew up.

In 2002 a Bra Boys Christmas bash turned into a riot when it coincided with a party for off-duty police at a Sydney social club.

One officer said: “The police copped an absolute flogging.”

The gang was also implicated in 2005 beach race riots.

Koby – who once dated Hollywood babe Tara Reid and was linked with Paris Hilton – said of Crowe: “He’s just like one of the boys. He’s risking big money and his reputation hanging out with us.”

Crowe said: “It is a compelling story that deserves to be told. These guys have grown up in testing circumstances and their humour and humanity are all the more impressive because of that.”